Loss of ovarian function accelerates the risk of cardiovascular and metabolic disease, and heralds the onset of changes that can have far-reaching consequences on women's future health. We will examine the impact of the menopause transition on several metabolic and cardiovascular risk factors associated with declining health status in women. Our overall hypothesis is that women who experience a natural menopause transition will show - accelerated decline in daily energy expenditure, increase in total and Intra-abdominal body fat and decline in insulin sensitivity. In this 5-year longitudinal study, we will recruit 57 premenopausal women and examine their natural history as they traverse the menopause. Changes in energy expenditure, body composition, body fat distribution and insulin sensitivity will be measured annually (a total of five exams) to examine the time course of menopause and age-related changes in outcome variables. Our First Aim will examine the effects of the menopause transition on total daily energy expenditure, body fat distribution and insulin sensitivity. We will use: 1) doubly labeled water and indirect calorimetry to measure changes in total daily energy expenditure, resting metabolic rate, thermic effect of a meal and physical activity; 2) computerized tomography to assess changes in intra-abdominal body fat and 3) euglycemic clamps to measure insulin sensitivity. Our Second Aim is to develop and cross-validate new models to predict daily energy requirements, as derived from biological markers of total daily energy expenditure in pre- and postmenopausal women and to compare them to current daily energy intake recommendations. Current recommendations for daily energy needs are based on out- dated food intake data and have not considered the influence of menopause status, body composition and physical activity as determinants of daily energy needs. These limitations have led to the suggestion that prescription of daily energy requirements should be based on the measurement of total daily energy expenditure. Analyses of these data will characterize the biological and metabolic sequelae of changes in energy metabolism, body fat distribution and insulin sensitivity in women as they traverse the menopause. Furthermore, we will offer new guidelines to predict energy requirements during the menopause transition.